1. Field of the Invention
The present invention relates to a speed control circuit for a DC motor comprising a pulse transmitter which emits a binary speed signal proportional to the speed of the DC motor.
2. Description of the Prior Art
In printer facilities, for example, the printer carriage is driven by a DC motor. Given standard speed control circuits for DC motors in printer drives, the speed control occurs via the armature voltage by way of analogously operating voltage control circuits. The actual speed is thereby converted into a speed-proportional voltage by a pulse transmitter connected to the motor shaft and by a frequency-to-voltage converter. The speed-proportional voltage is compared to a reference voltage which corresponds to the desired speed and the voltage difference is employed for controlling the armature voltage.
Other speed control circuits which have previously been proposed employ phase-locked loops for controlling the armature current. The actual speed of the DC motor is thereby acquired by a pulse transmitted connected to the motor shaft and is compared to a reference frequency which corresponds to the desired speed. The phase difference thereby arising is employed for controlling the armature current.
In these speed control circuits, a controlled acceleration up to a constant speed or, respectively, a controlled deceleration down to standstill is not provided. The start-up or, respectively, braking path which is subject to very pronounced errors due to frictional and voltage fluctuations was thereby dimensioned such that the electromotive force assures reliable operation given unfavorable friction and a generational braking effect.